1. Field of the Invention
The present invention relates to a signal/vibration detecting technique employing optical interference. The technique emits lights into open ends of a loop made of a plurality of optical fibers so that the lights are propagated clockwise and counterclockwise, respectively, through the loop, couples the propagated lights together so that they interfere with each other, and detects a physical change such as vibration applied to the loop by observing a change in the intensity of the interfering lights.
The present invention also relates to a technique of applying the signal/vibration detecting technique to identify a target optical fiber cable among many during, for example, cable changing and removing work.
The present invention also relates to a technique of applying the signal/vibration detecting technique to identify a target optical fiber among optical fibers contained in a cable and use the identified target optical fiber to carry out a conversation without cutting the optical fiber.
2. Description of the Prior Art
Various sensors and detectors that use optical interference caused on optical fibers and lasers have been proposed. For example, a Mach-Zhehnder interferometer emits a laser light from a light source, splits the laser light into two so that the two split lights pass through two optical paths, couples the lights so that they interfere with each other, and detects a phase shift between the lights according to a change in interference fringes.
This technique is applicable to provide a simple structure consisting of a laser and a loop made of a plurality of optical fibers to detect a physical change such as vibration applied to the loop.
The technique is also applicable to identify a target optical fiber cable among many, or identify a target optical fiber among optical fibers contained in a cable and carry out a conversation through the target optical fiber.
This technique is applicable to changing and removing work of optical fiber cables in a telephone tunnel or a manhole. During such work, the technique is used to identify a target optical fiber cable among many cables so that erroneous cables may not be cut. When changing an optical fiber to another in a given cable, the technique is used to identify the target optical fiber among many optical fibers contained in the cable.
To identify a target optical fiber cable, a prior art emits a light into an end of the cable, applies ultrasonic waves to the cable, monitors polarization of the light propagated through the cable influenced by the ultrasonic waves, and identifies the cable.
Another prior art emits a light from a light source and splits it into two by an optical coupler. The split lights are made incident to two different optical fibers contained in a target optical fiber cable. The split lights are propagated through the optical fibers, are coupled together by an optical coupler at the other end of the cable, and are received by a photo-detector. Vibration is applied to the cable. The vibration causes stress on the cable to change the lengths of optical paths through which the split lights are propagated. This changes a phase difference and polarization plane between the propagated lights, thereby changing the intensity of interference of the coupled lights at the end of the cable. According to this change, the cable is identified even if it is laid among many cables.
These prior arts are applicable to identify a target optical fiber among optical fibers contained in a cable.
The prior arts mentioned above must change polarization planes to identify a target optical fiber cable or a target optical fiber. If there is an outside factor to change polarization planes, the prior arts are unable to correctly identify the target cable or fiber. As a result, the prior arts achieve only a poor probability of 70% in identifying a target cable or fiber. This probability will further deteriorates depending on the material of a target cable or fiber. In addition, the prior arts require expensive devices.
The prior arts malfunction when the difference between the lengths of two optical fibers for propagating lights exceeds a coherent length. The prior arts need an additional optical coupler be installed at the receiver side of a cable, and if lights propagated through two optical fibers in the cable are polarized orthogonally, do not work because no interference occurs between the propagated lights.
On the other hand, the signal/vibration detecting technique of the present invention employs a simple, low-cost structure to surely identify a target optical fiber cable or a target optical fiber.
A target optical fiber identified according to any one of the techniques mentioned above can be used without being cut to carry out a conversation between distant work sites during cable/fiber changing and removing work.
To achieve such conversation, a prior art bends the target optical fiber to cause a loss, changes the radius of the bend, and uses brightness modulation due to the radius change. Another prior art distorts the optical fiber and uses a change in polarization of the optical fiber due to the distortion.
The prior art using brightness modulation applies vibration with, for example, a speaker to the optical fiber to change the radius of the bend formed on the optical fiber. The change in the radius changes a loss to change brightness, thereby modulating a light passed through the optical fiber. This technique is employed by an optical conversation method disclosed in Japanese Unexamined Patent Publication No. 4-368629 and by an optical fiber bend setting method for an optical fiber conversation apparatus disclosed in Japanese Unexamined Patent Publication No. 5-264909.
Japanese Unexamined Patent Publication No. 7-38502 discloses an optical fiber conversation apparatus that makes lights enter into and exit from the side of an optical fiber. A transmitter emits a light from a light source, modulates the brightness of the light, and makes the light incident to a bend of the optical fiber. A receiver converts leakage lights from a bend of the optical fiber into an electric signal.
The technique of the Japanese Unexamined Patent Publication No. 4-368029 vibrates a bend of an optical fiber to change the brightness of a light, thereby modulating the light. The degree of modulation of this technique is 9%, which is very low, and therefore, must be compensated. In addition, vibrating an optical fiber needs a complicated mechanism to increase the size and cost of the technique.
The technique of the Japanese Unexamined Patent Publication No. 7-38502 makes a light enter into and exit from the side of an optical fiber, to cause large optical coupling losses. As a result, this technique is unable to realize a large dynamic range and clear conversation.
The technique of changing polarization planes by ultrasonic waves is unable to secure a conversation if external factors make the polarization planes orthogonal to each other.
On the other hand, the signal/vibration detecting technique of the present invention employs a simple, inexpensive structure to improve the degree of modulation and reduce mechanical load on an optical fiber that is used for conversation.
An object of the present invention is to provide a signal/vibration detecting technique employing optical interference and a simple structure made of a laser and a loop of a plurality of optical fibers.
Another object of the present invention is to provide a technique of identifying a target optical fiber cable among many with the use of the signal/vibration detecting technique employing optical interference and a simple, inexpensive apparatus.
Still another object of the present invention is to provide a technique of identifying a target optical fiber among many and using the identified optical fiber to carry out a conversation at an improved degree of modulation and reduced load on the optical fiber, with the use of the signal/vibration detecting technique.
In order to accomplish the objects, a first aspect of the present invention provides an apparatus for detecting a signal based on optical interference, having a light source, a photo-detector, a loop made of a plurality of optical fibers and having open ends, and a splitter-coupler connected to the open ends of the loop. The light source emits a light, which is split by the splitter-coupler. The split lights are made incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop. The oppositely propagated lights are coupled by the splitter-coupler so that they interfere with each other. The interfering lights are converted by the photo-detector into a signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights.
According to the signal from the photo-detector, the first aspect detects a physical change applied to the loop and changed the phase difference between the oppositely propagated lights.
A second aspect of the present invention provides a method of detecting a signal based on optical interference, including the steps of emitting a light from a light source, splitting the light by a splitter-coupler, making the split lights incident to open ends of a loop made of a plurality of optical fibers so that the split lights are oppositely propagated through the loop, coupling the propagated lights by the splitter-coupler so that they interfere with each other, converting the interfering lights by a photo-detector into a signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights, and detecting, according to the signal from the photo-detector, a physical change applied to the loop and changed the phase difference between the lights.
A third aspect of the present invention adds, to the method of the second aspect, the step of inserting a delay unit in the loop or between the loop and the splitter-coupler, to delay the lights propagated through the loop.
Even if being applied to the midpoint of the loop, the physical change surely causes, due to the delay unit, a phase difference between the lights oppositely propagated through the loop, and therefore, is surely detectable according to the signal provided by the photo-detector.
A fourth aspect of the present invention provides an apparatus for detecting vibration based on optical interference, having a light source, a photo-detector, a loop made of a plurality of optical fibers and having open ends, and a splitter-coupler connected to the open ends of the loop. The light source emits a light, which is split by the splitter-coupler. The split lights are made incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop. The oppositely propagated lights are coupled by the splitter-coupler so that they interfere with each other. The interfering lights are converted by the photo-detector into a signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights caused by vibration applied to the loop.
According to the signal from the photo-detector, the fourth aspect detects a physical change, i.e., vibration applied to the loop and changed the phase difference between the oppositely propagated lights.
A fifth aspect of the present invention provides a method of detecting vibration based on optical interference, including the steps of emitting a light from a light source, splitting the light by a splitter-coupler, making the split lights incident to open ends of a loop made of a plurality of optical fibers so that the split lights are oppositely propagated through the loop, coupling the oppositely propagated lights by the splitter-coupler so that they interfere with each other, converting the interfering lights by a photo-detector into a signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights, and detecting, according to the signal from the photo-detector, vibration applied to the loop and changed the phase difference between the lights.
A sixth aspect of the present invention adds, to the method of the fifth aspect, the step of inserting a delay unit in the loop or between the loop and the splitter-coupler, to delay the lights oppositely propagated through the loop.
Even if being applied to the midpoint of the loop, the vibration surely causes, due to the delay unit, a phase difference between the lights oppositely propagated through the loop, and therefore, is surely detectable according to the signal from the photo-detector.
A seventh aspect of the present invention provides an apparatus for identifying a target optical fiber cable among many, having a light source, a photo-detector, a loop made of a plurality of optical fibers and having open ends, and a splitter-coupler. The splitter-coupler is connected to the light source, the photo-detector, and the open ends of the loop. The light source emits a light. The splitter-coupler receives the light, splits the light, makes the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, receives the oppositely propagated lights, couples the received lights so that they interfere with each other, and supplies the interfering lights to the photo-detector. The photo-detector converts the interfering lights into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights. According to the electric signal, the seventh aspect detects a physical change applied to the target optical fiber cable that contains at least a part of the loop.
An eighth aspect of the present invention provides an apparatus for identifying a target optical fiber cable among many, having a light source, a photo-detector, a loop made of a plurality of optical fibers and having open ends, and a splitter-coupler. The splitter-coupler is connected to the light source, the photo-detector, and the open ends of the loop. The light source emits a light, which is received by the splitter-coupler. The splitter-coupler splits the light, makes the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, receives the oppositely propagated lights, couples the received lights so that they interfere with each other, and supplies the interfering lights to the photo-detector. The photo-detector converts the interfering lights into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights. According to the electric signal, the eighth aspect detects vibration applied to the target optical fiber cable that contains at least a part of the loop.
A ninth aspect of the present invention provides an apparatus for identifying a target optical fiber cable among many, having an optical transceiver connected to open ends of a loop made of a plurality of optical fibers and a local unit for applying vibration to loop. The optical transceiver has a light source for emitting a light, a splitter-coupler for splitting the light, making the split lights incident to the open ends of the loop, respectively, so that the lights are oppositely propagated through the loop, receiving the oppositely propagated lights, and coupling the received lights so that they interfere with each other, and a photo-detector for converting the interfering lights into an electric signal. This electric signal indicates the intensity of the interfering lights, is responsive to a change in the phase difference between the lights caused by the vibration applied to the loop, and is used to identify the target optical fiber cable that contains at least a part of the loop.
Any one of the seventh to ninth aspects of the present invention picks up a plurality of optical fibers in a target optical fiber cable, or at least one of them in a target optical fiber cable and others in another optical fiber cable. Each end of the picked-up optical fibers is connected to each other into a loop having two open ends.
The light source emits a light. The splitter-coupler splits the light and makes the split lights incident to the open ends of the loop, respectively, so that the lights are oppositely propagated through the loop. The oppositely propagated lights are received and coupled by the splitter-coupler to that they interfere with each other. The interfering lights are supplied to the photo-detector.
Under this state, the local unit applies a physical change, which may be pressure, bend, tension, or vibration, to optical fiber cables including the target cable one after another.
The photo-detector converts the interfering lights from the splitter-coupler into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights. When the local unit applies the physical change to the target optical fiber cable that contains at least a part of the loop, the signal from the photo-detector shows a change corresponding to the physical change. As a result, one can identify the target optical fiber cable among many cables.
A tenth aspect of the present invention provides a method of identifying a target optical fiber cable among many, including the steps of connecting each end of a plurality of optical fibers to each other to form a loop having two open ends, connecting an optical transceiver to the open ends of the loop, emitting a light from a light source of the optical transceiver, splitting the light by a splitter-coupler of the optical transceiver, making the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, coupling the oppositely propagated lights so that they interfere with each other, converting the interfering lights by a photo-detector of the optical transceiver into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights, and detecting in the electric signal a physical change applied to the target-optical fiber cable that contains at least a part of the loop.
An eleventh aspect of the present invention provides a method of identifying a target optical fiber cable among many, including the steps of connecting each end of a plurality of optical fibers to each other to form a loop having two open ends, connecting an optical transceiver to the open ends of the loop, emitting a light from a light source of the optical transceiver, splitting the light by a splitter-coupler of the optical transceiver, making the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, coupling the oppositely propagated lights so that they interfere with each other, converting the interfering lights by a photo-detector of the optical transceiver into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights, and detecting, in the electric signal, vibration applied to the target optical fiber cable that contains at least a part of the loop.
A twelfth aspect of the present invention adds, to any one of the tenth and eleventh aspects, the step of inserting a delay unit in the loop or between the loop and the optical transceiver, to delay the lights oppositely propagated through the loop.
Even if being applied to the midpoint of the loop, the physical change or vibration surely causes a phase difference between the lights oppositely propagated through the loop, and therefore, is surely detectable according to the signal from the photo-detector.
A thirteenth aspect of the present invention provides an apparatus for identifying a target optical fiber among many, having a light source, a photo-detector, a loop made of a plurality of optical fibers and having open ends, and a splitter-coupler. The splitter-coupler is connected to the light source, the photo-detector, and the open ends of the loop made of the a plurality of optical fibers including the target optical fiber. The light source emits a light. The splitter-coupler splits the light, makes the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, receives the oppositely propagated lights, couples the received lights so that they interfere with each other, and supplies the interfering lights to the photo-detector. The photo-detector converts the interfering lights into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights. According to the electric signal, the thirteenth aspect detects a physical change applied to loop.
A fourteenth aspect of the present invention provides an apparatus for identifying a target optical fiber among many, having a light source, a photo-detector, a loop made of a plurality of optical fibers and having open ends, and a splitter-coupler. The splitter-coupler is connected to the light source, the photo-detector, and the open ends of the loop made of the a plurality of optical fibers including the target optical fiber. The light source emits a light. The splitter-coupler splits the light, makes the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, receives the oppositely propagated lights, couples the received lights so that they interfere with each other, and supplies the interfering lights to the photo-detector. The photo-detector converts the interfering lights into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights. According to the electric signal, the fourteenth aspect detects vibration applied to the loop.
A fifteenth aspect of the present invention provides an apparatus for identifying a target optical fiber among many, having an optical transceiver and a local unit. The optical transceiver is connected to open ends of a loop made of a plurality of optical fibers including the target optical fiber. The local unit applies vibration to the loop. The optical transceiver has a light source for emitting a light, a splitter-coupler for splitting the light, making the split lights incident to the open ends of the loop, respectively, so that the lights are oppositely propagated through the loop, receiving the oppositely propagated lights, and coupling the received lights so that they interfere with each other, and a photo-detector for converting the interfering lights into an electric signal. The electric signal indicates the intensity of the interfering lights, is responsive to a change in the phase difference between the lights caused by the vibration applied to the loop, and is used to identify the target optical fiber.
Any one of the thirteenth to fifteenth aspects of the present invention picks up a target optical fiber and another optical fiber in a given cable, connects one ends of the picked-up optical fibers to each other through an optical connector to form a loop having two open ends. The light source emits a light. The splitter-coupler splits the light and makes the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop. The oppositely propagated lights are received and coupled by the splitter-coupler so that they interfere with each other. The interfering lights are supplied to the photo-detector.
Under this state, the local unit applies a physical change, which may be pressure, bend, tension, or vibration, to optical fibers in the cable one after another.
The photo-detector converts the interfering lights into an electric signal that indicates the intensity of the interfering lights. When the local unit applies the physical change to the target optical fiber, the signal from the photo-detector shows a change corresponding to the physical change. As a result, one can identify the target optical fiber.
A sixteenth aspect of the present invention provides a method of identifying a target optical fiber among many, including the steps of connecting each end of a plurality of optical fibers including the target optical fiber to each other to form a loop having two open ends, connecting an optical transceiver to the open ends of the loop, emitting a light from a light source of the optical transceiver, splitting the light by a splitter-coupler of the optical transceiver, making the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, coupling the oppositely propagated lights so that they interfere with each other, converting the interfering lights by a photo-detector of the optical transceiver into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights, and detecting in the electric signal a physical change applied to the loop.
A seventeenth aspect of the present invention provides a method of identifying a target optical fiber among many, including the steps of connecting each end of a plurality of optical fibers including the target optical fiber to each other to form a loop having two open ends, connecting an optical transceiver to the open ends of the loop, emitting a light from a light source of the optical transceiver, splitting the light by a splitter-coupler of the optical transceiver, making the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, coupling the oppositely propagated lights so that they interfere with each other, converting the interfering lights by a photo-detector of the optical transceiver into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights, and detecting, in the electric signal, vibration applied to the loop.
An eighteenth aspect of the present invention adds, to any one of the sixteenth and seventeenth aspects, the step of inserting a delay unit in the loop or between the loop and the optical transceiver, to delay the lights propagated through the loop.
Even if being applied to the midpoint of the loop, the physical change or vibration surely causes a phase difference between the lights oppositely propagated through the loop, and therefore, is surely detectable according to the signal from the photo-detector.
A nineteenth aspect of the present invention provides an optical fiber communication apparatus having an optical transceiver connected to open ends of a loop made of a plurality of optical fibers including a target optical fiber, and a local unit attached to the loop. The optical transceiver has a light source for emitting a light, a first microphone for converting a voice into an electric signal, a driver for modulating the light from the light source according to the electric signal from the first microphone, a splitter-coupler for splitting the light from the light source, making the split lights incident to the open ends of the loop, respectively, so that the lights are oppositely propagated through the loop, receiving the oppositely propagated lights, and coupling the received lights so that they interfere with each other, a first photo-detector for converting the interfering lights into an electric signal, and a first voice unit for demodulating the electric signal from the first photo-detector into a voice signal. The local unit has a bender for bending the loop, a second photo-detector for receiving leakage lights from the bend of the loop and converting them into an electric signal, a second voice unit for demodulating the electric signal from the second photo-detector into a voice signal, a second microphone for converting a voice into an electric signal, and a vibrator for applying vibration to the loop according to the electric signal from the second microphone.
At a first work point at the open ends of the loop, the first microphone converts a voice into an electric signal, and the driver modulates a light from the light source according to the electric signal. The splitter-coupler splits the light from the light source and makes the split lights incident to the open ends of the loop. At a second work point where the local unit is installed, the bender bends the loop, the second photo-detector receives leakage lights from the bend and converts them into an electric signal, and the second voice unit demodulates the electric signal into a voice signal.
At the second work point, the second microphone converts a voice into an electric signal, and the vibrator vibrates the loop according to the electric signal. At this time at the first work point, the splitter-coupler couples the lights oppositely propagated through the loop to make the lights interfere with each other. The first photo-detector converts the interfering lights into an electric signal that indicates the intensity of the interfering lights and is responsive to a change in the phase difference between the lights. The first voice unit demodulates the electric signal into a voice signal, which is used to reproduce the voice entered by the local unit.
The nineteenth aspect enables the first and second work points to carry out a conversation between them through the loop once the target optical fiber that forms a part of the loop is identified.
A twentieth aspect of the present invention structures the apparatus of the nineteenth aspect such that the driver of the optical transceiver FM-modulates a light from the i light source, the first voice unit of the optical transceiver AM-demodulates a signal from the first photo-detector into a voice signal, and the second voice unit of the local unit FM-demodulates a signal from the second photo-detector into a voice signal.
The twentieth aspect differently modulates and demodulates a signal from the optical transceiver to the local unit and a signal from the local unit to the optical transceiver so that each of the optical transceiver and local unit can clearly reproduce a voice signal sent from the opposite party without crosstalk.
A twenty-first aspect of the present invention provides an optical fiber communication method including the steps of connecting each end of a plurality of optical fibers to each other through an optical connector to form a loop having two open ends, connecting an optical transceiver to the open ends of the loop, attaching a local unit to the loop between the optical transceiver and the optical connector, and carrying out optical-transceiver steps and local-unit steps. The optical-transceiver steps include emitting a light from a light source, converting a voice into an electric signal by a first microphone, modulating the light from the light source by a driver according to the electric signal from the first microphone, splitting the light from the light source by a splitter-coupler, making the split lights incident to the open ends of the loop, respectively, so that the split lights are oppositely propagated through the loop, coupling the oppositely propagated lights by the splitter-coupler so that they interfere with each other, converting the interfering lights into an electric signal by a first photo-detector, and demodulating the electric signal into a voice signal by a first voice unit. The local-unit steps include bending the loop, receiving leakage lights from the bend by a second photo-detector, converting the leakage lights by the second photo-detector into an electric signal, demodulating the electric signal into a voice signal by a second voice unit, converting a voice into an electric signal by a second microphone, and vibrating the loop by a vibrator according to the electric signal from the second microphone, thereby carrying out a conversation between the optical transceiver and the local unit.
A twenty-second aspect of the present invention adds, to the twenty-first aspect, the step of inserting a delay unit in the loop or between the loop and the optical transceiver, to delay the lights propagated through the loop.
Even if the second work point is at the midpoint of the optical-fiber loop, the twenty-second aspect surely causes a phase difference between the lights oppositely propagated through the loop and surely detects a signal applied to the loop by the local unit, according to the signal from the first photo-detector.
A twenty-third aspect of the present invention adds, to any one of the twenty-first and twenty-second aspects, the steps of FM-modulating a light from the light source by the driver of the optical transceiver, AM-demodulating a signal from the first photo-detector into a voice signal by the first voice unit of the optical transceiver, and FM-demodulating a signal from the second photo-detector into a voice signal by the second voice unit of the local unit.
This aspect employs different modulation techniques for a signal from the optical transceiver to the local unit and for a signal from the local unit to the optical transceiver, so that each of the optical transceiver and local unit may clearly reproduce voice from a signal sent from the opposite party without crosstalk.
Other and further objects and features of the present invention will become obvious upon an understanding of the illustrative embodiments about to be described in connection with the accompanying drawings or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employing of the invention in practice.